This project is intended to provide an understanding of factors that influence the development of rat renal proximal tubule amino acid recovery using the Beta-amino acid, taurine, as a transport probe. The accumulation of taurine and its transport characteristics will be examined using in-vivo clearance studies in parallel with amino acid uptake studies in-vitro using think cortex slices, collagenase isolated cortical tubules and isolated membrane preparations. Animals of varying ages between birth and maturity will be used and once the age related patterns of transport are known the influence on transport of agents such as parathyroid hormone, dibutyryl cAMP, cAMP, increased taurine dietary load to both nursing mother and immature rats and diminished dietary taurine load will be ascertained. During the current year we had planned to examine the uptake and efflux of taurine in isolated tubule segments from rats of different ages who have been treated with a high taurine diet, examine the differences between adult and newborn animals in terms of their differential response to dibutyryl cyclic AMP, develop assays for marker enzymes for kidney cortex and brush borders, prepare brush border membranes, and measure the accumulation of taurine by brush border membranes. Studies in 1979 have examined the adaptation of amino acid transport by kidney cortex to an altered dietary load of taurine. We have used two special diets in Sprague-Dawley rats to examine adaptation: (1) a 3% taurine diet that allows one to give a high taurine load and (2) a diet deficient in methiionine, cystine, cysteine and taurine. Excretion of taurine in enhanced in-vivo by the high taurine diet and reabsorption is increased after the low taurine diet when compared to the normal diet. The reabsorption of taurine rose 95% in animals on a normal diet to 99.6% in animals on a low taurine diet, despite no change in filtered taurine load (i.e. the same plasma taurine level in all 3 groups of animals) urine taurine (micron moles/mg creatinine) is 6-fold higher in normals than in low taurine animals.